The Cincinnati Comprehensive Sickle Cell Center, based in the Division of Hematology/Oncology. at Children's Hospital Medical Center and affiliated with the University of Cincinnati College of Medicine, provides a full range of clinical services to people affected by sickle cell disease. Building on the finding that elevated homocysteine (Hcy) in sickle cell patients is associated with pyridoxine deficiency, an inter-Center collaborative research proposal examines the correlation of elevated Hey with activation of coagulation and endothelial cells in patients, and tests whether pyridoxine supplementation corrects these abnormalities. An interactive research team with expertise in molecular biology, membrane transport, in vivo cell kinetics, and clinical research will pursue projects focused on SS RBC dehydration, a key factor in sickle cell pathology, which results from two abnormal transport pathways, KCl cotransport (KCC) and sickling-induced cation leaks. The clinical study of Project 2 tests the therapeutic potential of dipyridamole, which inhibits sickling-induced cation leaks, and magnesium, which inhibits KCC, to improve SS RBC hydration in vivo. Project 3 examines the rate and mechanisms of hydration changes of SS RBC in vivo, using biotin label techniques unique to this Center. Project 4 explores the molecular basis of post-translational regulation of KCC by cell volume in normal and SS RBC. Project 5 focuses on the erythroid isoforms of KCC and their transcriptional regulation. A Clinical Core includes Pediatric and Adult Progra ms to provide comprehensive services to over 375 patients, to support basic and clinical research efforts, and to participate in inter-Center collaborative trials. An Education and Patient Services Core provides educational and psychosocial support for patients and families, and includes a Transition Program bridging the Pediatric and Adult Clinical Programs, in collaboration with the Sickle Cell Awareness Group and the Urban League of Cincinnati. An Administrative Core provides overall fiscal and programmatic management and serves as the focal point for Center activities, programs, and communication. The projects and cores in this proposal will be integrated with independently funded programs of newborn hemoglobinopathy screening follow-up, education and counseling, a Hemoglobin Diagnostic Laboratory, and other basic science and clinical research projects. The Cincinnati comprehensive Sickle Cell Center is poised to lead in the national effort to develop and test new therapies for sickle cell disease to improve the lives of affected individuals.